#define_GNU_SOURCE /* See feature_test_macros(7) */
#include<fcntl.h>ssize_ttee(intfd_in,intfd_out,size_tlen,unsignedintflags);
tee() duplicates up to len bytes of data from the pipe referred to by
the file descriptor fd_in to the pipe referred to by the file
descriptor fd_out. It does not consume the data that is duplicated
from fd_in; therefore, that data can be copied by a subsequent
splice(2).